1. Field of the Invention
The present invention relates to an apparatus and method for generating a Media Access Control (MAC) Protocol Data Unit (MPDU) in a wireless communication system. More particularly, the present invention relates to an apparatus and method for generating a header or sub-header that represents MAC Service Data Unit (MSDU) information constituting an MPDU in a wireless communication system.
2. Description of the Related Art
In a wireless communication system, a MAC layer of a transmit end processes MSDUs received from an upper layer and generates an MPDU for transmission to a lower layer. For example, in the Institute of Electrical and Electronics Engineers (IEEE) 802.16 standard, the transmit end generates an MPDU as illustrated in FIGS. 1A through 1D.
FIGS. 1A through 1D illustrate a construction of an MPDU in a wireless communication system according to the conventional art.
As illustrated in FIG. 1A, a MAC layer of a transmit end receives three MSDUs from an upper layer. After that, as illustrated in FIG. 1B,the transmit end fragments the MSDUs into Automatic Repeat reQuest (ARQ) blocks of a fixed length. At this time, the length of the ARQ block fragmenting the MSDU in the transmit end is commonly applied to all receive ends.
After that, as illustrated in FIG. 1C the transmit end constructs an MPDU with the fragmented ARQ blocks. For example, the transmit end constructs a first MPDU with an ARQ block #1 to an ARQ block #3, constructs a second MPDU with an ARQ block #4 to an ARQ block #9, and constructs a third MPDU with an ARQ block #10 to an ARQ block #13.
If constructing the MPDUs as illustrated in FIG. 1C, one MPDU includes parts from one or more MSDUs. For example, the second MPDU includes a part of an MSDU #1, a part of an MSDU #2, and a part of an MSDU #3.
Thus, the transmit end adds a Fragmentation Sub-Header (FSH) or Packing Sub-Header (PSH), which includes MSDU information constituting each MPDU, to each MPDU so that the receive end can reconstruct an MSDU using the MPDUs. At this time, the transmit end adds the FSH to an MPDU composed of one MSDU or a part of the MSDU, and adds the PSH to an MPDU composed of two or more MSDUs or two or more fragmented MSDUs. For example, the first MPDU of FIG. 1C consists of a part of the MSDU #1 and thus includes an FSH. The third MPDU consists of a part of the MSDU #3 and thus includes an FSH. The second MPDU of FIG. 1C consists of a part of the MSDU #1, the MSDU #2, and a part of the MSDU #3 and thus includes a PSH before each MSDU. Here, the FSH or PSH added to each MPDU includes the lowest ARQ Sequence Number (SN) among SNs of ARQ blocks constituting the MPDU.
If generating the MPDUs as in FIG. 1C, the transmit end constructs a PHYsical (PHY) Protocol Data Unit (PPDU) with the MPDUs as illustrated in FIG. 1D. For example, the transmit end constructs a first PPDU with the first MPDU and the second MPDU, and constructs a second PPDU with the third MPDU.
The receive end can identify MSDU information included in each MPDU using an FSH and PSH included in each MPDU, and reconstruct an MSDU. Also, if having knowledge of a length of the MPDU and a fixed length of an ARQ block, the receive end can be aware of the number of ARQ blocks included in each MPDU.
As described above, the transmit end constructs an MPDU with ARQ blocks of a fixed length fragmenting an MSDU. Thus, when a size of a physical layer resource allocated for data transmission is not a multiple of an ARQ block size, there is a problem that the transmit end fails to add an MPDU in a PPDU, thus wasting a resource.
A data throughput at a receive end is proportional to a size of an ARQ block. Thus, the receive end has to set the ARQ block large in size to increase the data throughput. However, in order to commonly apply a length of the ARQ block to all receive ends, the transmit end sets the ARQ block small in length so that it can provide service to a receive end having the worst channel condition. That is, if transmitting data to a receive end with a poor channel condition, the transmit end increases a transmission power and thus, cannot transmit a large amount of data at a time in a physical layer. Therefore, the transmit end sets an ARQ block size of a MAC layer small. Thus, there is a problem that a data throughput of the whole system is deteriorated.